In many situations there is a desire to monitor flow of fluid in conduits. For example in the oil and gas industry there is sometimes a desire to determine the flow rates of oil and gas through a production well at different parts of the well. The rate of flow of product at the top of the well can be relatively easily determined, for example by using a suitable flow meter. However the rate of flow at different depths into the well may be of interest. For example the rate of flow at different depths within the well may indicate the relative contribution to the total flow of the various different sections of the well which provide an inlet for the oil or gas. In addition the flow regime, for instance whether the flow is single phase or multi-phase or whether there is laminar flow or turbulent flow, may be of interest.
This may be useful for long term monitoring and/or to provide useful information for planning future wells. Also in some instances a well may be divided into a number of different production zones which are effectively owned or leased by different organisations. Thus there may be a need to determine the relative contribution to the total flow from each production zone.
The use of permanent flow meters at different depths within a well is not generally practical due to the difficulties in providing suitably rugged equipment that can survive the harsh conditions in a production well for long periods of time, and the difficulties in installing such equipment with a suitable power supply and means of relaying the flow information to the surface. Typically therefore flow readings are acquired periodically by inserting wire line tools having one or more flow meters into the well on a temporary basis and taking flow readings at different depths. However the use of wire line tools involves halting normal production and is a relatively expensive procedure.
It would therefore be desirable to be able to monitor production flow at different depths within a well in use without the need for inserting any special instruments into the flow. Similar consideration can apply in other fields of application, such as flow through sub-sea pipelines or pipelines in other locations without easy access.